1. Field of the Invention
Embodiments of the invention relate generally to photonic components, more particularly to passively-thermally-stabilized, ultra low power photonic interconnect apparatus and methods and, even more particularly to CMOS (Complementary Metal-Oxide-Semiconductor)-compatible apparatus, methods, and applications thereof.
2. Technical Background
Si nanophotonics enables CMOS-compatible systems consisting of optics and electronics in a single, highly integrated system. One of the exciting opportunities for Si nanophotonics is ultra low power interconnects leading to efficient and low power computing. In theory, optical interconnects can enable large bandwidths with low power owing to the large carrier frequency (200 THz) and to the fact that one can propagate light at frequencies at which silicon is transparent (no intrinsic losses). However ultralow power photonic interconnects compatible with current CMOS microelectronics have not yet been demonstrated, mainly because the power needed to stabilize these photonic components with temperature is prohibitively high, due to the high thermo-optic coefficient of silicon.
Most solutions proposed to overcome this problem are either power hungry or require materials that are not compatible with standard CMOS processing. Work has been reported on cladding silicon photonic structures with polymeric based materials with negative thermo-optic coefficient for thermal compensation. Since such materials have a negative thermo-optic coefficient in contrast to silicon, which has a positive thermo-optic coefficient, passive compensation was possible. Such structures, however, are currently not compatible with front-end CMOS processing due to the polymer, which is incompatible with such processing. Moreover, reliability is a major concern for commercial devices incorporating polymeric materials. Another reported approach uses local heating to dynamically stabilize the devices. This is done is several different ways—using external metal heaters, direct heating of the silicon device by alternating the bias current for an active device or, using silicon itself as a resistive material for heating. All of these approaches are active and require substantial space and power consumption, which often accounts for the largest share in power budget of state-of-the-art silicon photonics. M. Uenuma and T. Moooka, Temperature-independent silicon waveguide optical filter, Opt. Lett. 34, No. 5, 599-601 (2009) describe a Mach-Zehnder interferometer optical filter on a silicon-on-insulator substrate that theoretically could reduce its temperature-dependent wavelength shift to less than 1 pm/° C. by a selected combination of narrower and wider silicon waveguide arms of the Mach-Zehnder interferometer and, completely eliminate the temperature dependence if the appropriate combination of ΔL and L′ could be experimentally realized.
In view of the aforementioned shortcomings and disadvantages with the state of the art, the inventors have recognized the need for CMOS-compatible passive compensation of the thermo-optic effect in silicon photonic devices. There is particularly a need for being able to thermally stabilize resonant devices because resonant devices such as microring resonators are ideally suited for dense integration of optical networks due to their compact size, high extinction ratio per unit length, low insertion loss and low power consumption. Moreover, the recognized advantages and benefits obtainable by addressing this need and as provided by the embodied invention include, but are not limited to, complete control over the temperature sensitivity of silicon-integrated and, in particular, Mach-Zehnder, interferometers; athermal operation of closed-loop and, in particular, silicon-integrated, microring resonators; broadband operation over a wide temperature range, with less than 3 dB degradation in the overall extinction ratio; fully CMOS-compatible processing and manufacturing with complete passive thermal stabilization; and, self-stabilized photonic structures requiring no additional tuning power, which typically accounts for the largest share in the power budget of Si photonics.